1. Field of the Invention
The present invention relates to an antenna device, a battery pack with an antenna, and a communication terminal device each of which is available in a radio frequency identification (RFID) system or the like communicating with an external device through an electromagnetic field signal.
2. Description of the Related Art
In an RFID system in which a reader/writer and an RFID tag are caused to communicate with each other on the basis of a noncontact method and predetermined information is transmitted between the reader/writer and the RFID tag, each of the reader/writer and the RFID tag includes an antenna device used for transmitting and receiving a wireless signal. For example, in an HF band RFID system utilizing a 13.56 MHz band as a communication frequency, the antennae of the RFID tag and the reader/writer are configured using antenna coils, and an antenna coil on an RFID tag side and an antenna coil on a reader/writer side are coupled with each other mainly through an induction magnetic field.
In recent years, communication terminal devices such as mobile phones and the like have been equipped with antenna coils used for the HF band RFID system, and the communication terminal devices have been used as readers/writers or RFID tags, in many cases. However, within the chassis of the communication terminal device, conductive bodies (metal bodies) such as a liquid crystal display panel, a keyboard, an RF circuit substrate, a battery pack, and the like are provided. In addition, the induction magnetic field is prevented from being formed, owing to these conductive bodies, and it is difficult to secure a sufficient communication distance, in some cases.
Therefore, for example, as described in Japanese Patent No. 4013987, there has been known a structure in which an antenna device configured using an antenna coil and a magnetic material core is mounted on a circuit substrate and the end portion of the magnetic material core extends to wrap around the side surface of the circuit substrate.
Here, an example of the antenna device disclosed in Japanese Patent No. 4013987 will be illustrated in FIG. 1.
FIG. 1 is the perspective view of an antenna device 106. An antenna coil 206 is in close contact with and mounted on the main surface of a circuit substrate 1. The circuit substrate 1 is a substrate arranged at a predetermined position within a mobile phone terminal, and an RF circuit, a control circuit, and the like, not illustrated, are formed on the substrate. The circuit substrate 1 is arranged at a predetermined position within a chassis so to be parallel to the main surface of the mobile phone terminal. In addition, in the circuit substrate 1, on a surface facing a surface on which the antenna coil 206 is mounted, a ground electrode (not illustrated) is fully formed.
The antenna coil 206 is configured using a magnetic material core 60 and a coil 70. The magnetic material core 60 includes a first main surface and a second main surface, the first main surface and the second main surface face each other, and the second main surface faces the circuit substrate. In addition, on both the end portions of the magnetic material core 60, bending portions 61 and 62 along the side surfaces of the circuit substrate 1 are formed. Namely, the magnetic material core 60 is bent in the vicinities of the side surfaces of the circuit substrate 1.
On the first main surface of the magnetic material core 60, which does not face the circuit substrate 1, the coil 70 is formed using a coil conductor 65. The coil axis of the coil 70 is perpendicular to the first main surface. At the center of the coil 70, an aperture portion 63 in which no coil conductor 65 is formed is provided. A through hole is provided at a conductor end 66 of the coil 70, and an electrode provided on a surface of the circuit substrate 1 facing the antenna coil 206 and the conductor end 66 of the coil 70 are electrically connected to each other owing to soldering, thereby being finally connected to a terminal 7. A conductor end of the coil 70, which is located on a side opposite to the conductor end 66, is connected to a terminal 8. The terminals 7 and 8 are pattern electrodes formed on the circuit substrate 1, and connected to an RFID processing circuit on the circuit substrate 1, not illustrated.
According to this structure, it is possible to minimize the influence of such conductive bodies (metal bodies) as described above, and it is possible to secure a sufficient communication distance.